The present invention is directed to a process for performing a chemical reaction, to a process for separating water from a mixture containing water, to a membrane suitable for such processes and to a process for preparing a membrane.
Modern chemical engineering has a focus on the integration of reaction and separation. In-situ separation of water from the Fischer-Tropsch reaction mixture is an example of such integration. The continuous removal of water, which is produced as a side product, contributes to an improvement of conversion, product selectivity and catalyst life time.
More in general it can be remarked, that the removal of water from mixtures with water is a very important aspects in various areas of chemical engineering and process technology. In reactions where water is a by-product, be it an equilibrium reaction or a non-equilibrium reaction, the continuous removal of water produced, from the reaction mixture helps to improve the reaction efficiency.
Separating of water from mixtures thereof, more in particular with H2, CO, CO2, CH4 and higher alkanes, is also very important, more in particular in case the other component(s) need(s) to be dry, for example for further reaction or use.
Separation can be based on several principles. With a hydrophilic membrane, it is possible to separate water from for example a mixture of water and an organic component. The separation principle is based on the preference of the membrane for adsorbing water. Also separation on size is possible, when the components to be separated are small enough in kinetic diameter to migrate through the zeolite pores and the components from which they have to be separated have a kinetic diameter that is too large.
The kinetic diameter can be understood as the diameter of a pore needed to let that specific molecule pass. Water has a kinetic diameter of 2.65 Å, even smaller than that of hydrogen. Thus separation based on geometry is possible, when one finds a zeolite with a pore size large enough to enable water to pass and to exclude hydrogen and other larger molecules. It was generally assumed that 6-membered rings were unsuitable for this type of separation.
In most chemical reactions with water as by-product, water has the smallest kinetic diameter. For example in a Fischer-Tropsch reaction mixture the kinetic diameters of H2, CO and linear alkanes are respectively 2.89, 3.76 and 4.3 Å.